1. Field of the Invention
The present invention relates generally to a vehicular suspension system and, more particularly, to a suspension control apparatus and method for controlling the operation of such a suspension system so as to suppress rolling and nose diving of a vehicle in response to an output signal from an acceleration sensor representative of a lateral or transverse acceleration of the vehicle.
2. Description of the Related Art
In the past, many suspension control apparatus of this type have been known, some examples of which are disclosed in Japanese Utility Model Laid-Open No. 61-163710 or Japanese Patent Laid-Open No. 62-34808. In these conventional suspension control apparatus, a fluid spring chamber such as a pneumatic spring chamber is interposed between each road wheel and the body of a vehicle so that supply to and discharge from the fluid spring chamber of compressed air is controlled in an appropriate manner to suppress rolling or nose diving of the vehicle body. Specifically, there is a tendency that when a vehicle is steered to turn, the suspension units disposed on the turning side of the vehicle are forced to contract under the action of centrifugal force whereas those on the opposite side thereof expand. In order to suppress this tendency, a predetermined amount of compressed air is supplied to the fluid spring chamber of each of the suspension units on the contracted side, and at the same time a predetermined amount of pressure air is discharged from the fluid spring chamber of each of the suspension units on the expanded side so as to incline the vehicle body in the opposite direction, thereby maintaining the attitude of the vehicle body in a horizontal manner.
To this end, the rolling condition such as the magnitude and direction of rolling of the vehicle body is detected by an acceleration sensor such as a G sensor in such a manner that the magnitude and direction of the rolling are determined according to a deviation in the right or left direction from a neutral point (i.e., the point of 0 G) of a sensing member of the acceleration sensor, and a control unit such as a microcomputer stores quantities of control parameters which correspond to the rolling condition thus detected and performs roll control based on the stored control quantities, In this case, however, if the direction of the transverse acceleration changes from the right to the left or vice versa in a short period of time, there will be the following drawbacks; no proper roll control can be effected due to time lags in controlling operation; and the suspension, thus resulting in deterioration in the durability thereof.
Moreover, if roll control is suddenly stopped in the presence of a variation in frequency of the change of direction of the transverse acceleration greater than a prescribed frequency level, there will be a possibility of losing proper roll controlling capability when the vehicle is steered to make a lane change or abrupt turn in emergency situations.